22 Questions
What is the characteristic of garnet and spinel that eliminates the need for cutters to consider pleochroism?
They are singly refractive
Which of the following is a mixture of pyrope and almandine?
Rhodolite
What is the primary source of rhodolite since the 1960s?
East Africa
What is the coloring agent in tsavorite?
Vanadium
What is the type of garnet that is often used in inexpensive, mass-market jewelry?
Pyrope-almandine
What is the chemical composition of demantoid?
A mixture of chromium and iron
What is the characteristic of color-change garnets?
They are pyrope-spessartine mixtures
What was previously identified as ruby but later recognized as spinel?
Many historically important red gems
What is the primary characteristic that distinguishes rhodolite from other red garnets?
Its dark purplish red to light reddish purple hue
Which type of garnet is typically classified by its physical and optical properties?
All garnets
What is the primary reason for the high value of large tsavorite stones?
Their rarity
What is the primary use of pyrope-almandine garnets?
In inexpensive, mass-market jewelry
What is the characteristic of demantoid that distinguishes it from other types of garnet?
Its presence of chromium and iron
Which type of garnet is often used as a substitute for ruby?
Spinel
What is the primary characteristic of color-change garnets?
Their mixture of pyrope and spessartine
What is the primary difference between hessonite and other types of garnet?
Its transparent orange to cinnamon-colored variety
Which type of garnet is typically mined in East Africa?
All of the above
What is the primary characteristic of garnets that distinguishes them from other minerals?
Their singly refractive nature
A cabochon that has a curved, undercut bottom, designed to lighten the tone of the gem is referred to as ?
Hollowback
When a chemical is substituted for another in the crystal structure of a mineral , what has happened?
Isomorphous Replacement
What is the most valuable orange garnet?
Spessartine
In Spinel, the higher the chromium content, the stronger what?
Red Hue
Study Notes
Garnet and Spinel
- Garnet and spinel are singly refractive, eliminating the need for cutters to consider pleochroism.
- Most red garnets, including the popular rhodolite, are mixtures of pyrope and almandine.
- Garnets belong to a group of minerals with the same crystal structure but slightly different chemical composition.
- Rhodolite, the most valuable red garnet, has a dark purplish red to light reddish purple hue.
- Many garnets are mixtures of two or more garnet species.
- Gemologists classify garnets by their physical and optical properties, but many dealers sell garnets on the basis of color or origin.
Garnet Species
- Hessonite is the transparent orange to cinnamon-colored variety of the grossular species.
Tsavorite
- Tsavorite is colored by vanadium, and the best is pure green or green with a slight amount of blue.
- Tsavorite is mined mostly in East Africa.
- Large tsavorite rough is extremely rare, so there’s a huge increase in value between small and large fashioned stones.
Spinel
- Many historically important red gems, long identified as ruby, were recognized as spinel in the 1800s.
- Demantoid, the transparent green variety of andradite, is colored by a mixture of chromium and iron.
Garnet Sources and Uses
- East Africa has been the most important source of rhodolite since the 1960s.
- Huge numbers of dark-toned, reddish brown, calibrated pyrope-almandine garnets are used in inexpensive, mass-market jewelry.
Garnet and Spinel
- Garnet and spinel are singly refractive, eliminating the need for cutters to consider pleochroism.
- Most red garnets, including the popular rhodolite, are mixtures of pyrope and almandine.
- Garnets belong to a group of minerals with the same crystal structure but slightly different chemical composition.
- Rhodolite, the most valuable red garnet, has a dark purplish red to light reddish purple hue.
- Many garnets are mixtures of two or more garnet species.
- Gemologists classify garnets by their physical and optical properties, but many dealers sell garnets on the basis of color or origin.
Garnet Species
- Hessonite is the transparent orange to cinnamon-colored variety of the grossular species.
Tsavorite
- Tsavorite is colored by vanadium, and the best is pure green or green with a slight amount of blue.
- Tsavorite is mined mostly in East Africa.
- Large tsavorite rough is extremely rare, so there’s a huge increase in value between small and large fashioned stones.
Spinel
- Many historically important red gems, long identified as ruby, were recognized as spinel in the 1800s.
- Demantoid, the transparent green variety of andradite, is colored by a mixture of chromium and iron.
Garnet Sources and Uses
- East Africa has been the most important source of rhodolite since the 1960s.
- Huge numbers of dark-toned, reddish brown, calibrated pyrope-almandine garnets are used in inexpensive, mass-market jewelry.
This quiz covers the characteristics and types of garnet and spinel, including their optical properties and species.
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